1. Field of the Invention
The present invention generally relates to an apparatus and method for preventing diffusion of a first fluid into the bulk of a second fluid filling a substantially closed chamber. The present invention is particularly useful in preventing diffusion of a gas under high pressure into the bulk of a liquid filling a substantially closed chamber. This system is particularly useful in test devices where the liquid is being pressurized to extremely high pressures by the gas and where test instruments extend through the liquid/gas interface to immerse sensors in the test liquid.
2. Description of the Background
It is often desirable to pressurize a liquid to extremely high pressures to perform a variety of tests on that liquid. For example, drilling fluids manufactured for use in deep drilling operations are often subjected in use to temperatures in excess of 450.degree. F. and pressures in excess of 10,000 psi. Accordingly, it is desirable to test these fluids under conditions simulating this harsh borehole environment.
It is possible to test these fluids simply by pumping them to the downhole location where the fluids are subjected to the downhole environment. A variety of tests are then conducted on the fluids after they are returned to the surface. However, because these tests are not conducted in the actual harsh conditions and the results may not reflect the characteristics of the fluid in the borehole environment, this testing method is unsatisfactory. These tests really only reflect changes which have occurred in the fluids as a result of the harsh borehole conditions.
It is desirable to test drilling fluids while they are actually in an environment simulating the harsh borehole conditions. Accordingly, it is desirable to be able to test these fluids at temperatures in excess of 450.degree. F. and at pressures in excess of 10,000 psi. These conditions are simulated by placing the fluid in a container including the test devices and sensors and subjecting the entirety to the simulated environment. Those skilled in the art will appreciate that this harsh environment is readily produced by placing the test equipment in a device which is heated to the test temperature by an appropriate autoclave and which is pressurized to the test pressure by the introduction of nitrogen or another inert gas. Because the inert gas is employed to pressurize the fluid, it must be in pressure communication therewith. Further, test sensors and devices extend into the liquid while various control equipment is typically maintained outside the liquid-containing vessel.
Because diffusion of the pressurizing gas into the test liquid results in changes in the physical characteristics of the liquid and, accordingly, alters the test results, it is desirable to exclude the pressurizing gas from the test liquid. However, the harsh conditions, extremely high pressure and high temperature, under which these tests are performed have made exclusion of the pressurizing gas from the test liquid a continuing problem. Conventional sealing means have not proved satisfactory. Accordingly, there has been a long felt but unfulfilled need within the industry for an apparatus and method for preventing diffusion of the pressurizing gas into the bulk of the test liquid.